Incubators are used in laboratories to maintain as viable bacteria, cells, tissues, and other biological specimens. Incubators accomplish this by providing a controlled environment. There are many parameters of the incubator environment which require control. These include temperature, humidity, and the concentration of gases such as oxygen and carbon dioxide, among others. An air circulation system is a vital ingredient in creating the correct environmental conditions for the growth of cell cultures in a laboratory incubator. Air circulation is needed to maintain temperature uniformity within the chamber and also to effectively distribute and mix the various gases, such as CO2 and N2, used to control the pH and O2 levels within the chamber. The air flow keeps the lighter gases from stratifying within the chamber and aids in the control of CO2 and O2 levels by providing air flow across the gas sensors. A blower is generally used in conjunction with a high efficiency particulate air or “HEPA” filter for circulating the air and removing contaminants from the air. The HEPA filters must be maintained at a temperature above the dew point of the air mixture to prevent condensation from developing inside the filter. This condensation can restrict or block the flow of air through the filter. Problems which existed with such air circulation systems included the requirement for an additional heat source to maintain the temperature of the HEPA filter above the dew point of the air mixture. Also, HEPA filters have generally been mounted in locations requiring the removal of side panels and other hardware associated with the incubator in order to access the filter for replacement. As the researcher or operator may be exposed to high voltage components when removing these incubator panels, a qualified service technician must be used for what should otherwise be a simple filter replacement procedure.
These problems were addressed in U.S. Pat. No. 5,792,427 by providing a HEPA filter located within the gaseous environment of the interior chamber of the incubator. As previously mentioned, the air flow pattern within the incubator is created by a high volume air blower mounted within the incubator chamber in an easily accessible manner. Air is pulled into a blower near the top of the chamber and exhausted through duct work that runs across the top of the chamber, down a plenum located behind a side wall of the chamber and across the bottom of the chamber until the air disperses and is pulled up vertically through perforated shelves located inside the chamber. In the preferred embodiment of U.S. Pat. No. 5,792,427, a HEPA filter is mounted directly to the blower and is located internally to the chamber. Therefore, the HEPA filter does not require an additional heat source to maintain its temperature above the dew point of the air mixture within the chamber. The HEPA filter is also easily removed and replaced by a researcher or other user from within the chamber and does not require the removal of side panels or other hardware which might involve exposure to high voltage wiring and/or components.
Thus, filtering the gaseous environment of an incubator to remove particulate materials, as with a HEPA filter, is known in the art. However, particulate materials are not the only potential source of contamination in an incubator. For example, volatile organic compounds (VOCs) may also be present within the incubator chamber. VOCs are not removed by a HEPA filter, and as such, could have a harmful effect on the samples within the incubator chamber.
There are many sources of VOCs. They may be present in the atmosphere of the room in which the incubator is located often in greater concentrations than air outside a laboratory. Sources of VOC contamination in the laboratory include general air contamination, cleaning agents, and off-gassing laboratory equipment and plasticware. VOCs include organics, such as alcohols, aldehydes, ketones, esters, aliphatics, aromatics and chlorinated hydrocarbons. When the incubator is opened, these VOCs may enter the incubator chamber. In addition to this means of contamination, the supply of gases such as carbon dioxide and oxygen to the incubator environment from an external supply may provide a direct path of ingress for the undesirable VOCs. Compounds and solutions used in culturing techniques may also contribute to contamination by unwanted VOCs.
It would thus be desirable to filter VOCs from the incubator in order to improve the quality of and to better control the atmosphere of the incubator. As an example of this, a system and method for filtering VOCs from incubators is disclosed in U.S. Pat. No. 6,013,119. According to the disclosure of that patent, there is provided a stand-alone filter system for an incubator for filtering VOCs and particulate material from the gaseous environment within the incubator. This system uses an inlet for receiving a gas stream from the gaseous environment of the incubator; an outlet for returning the gas stream to the gaseous environment of the incubator; and a filter connected between the inlet and outlet for filtering the stream of gas in order to filter VOCs and particulate material from the gas stream. In each embodiment of the incubator of U.S. Pat. No. 6,013,119, air is removed from the gaseous environment of the incubator cabinet at a low flow rate into a stand-alone filter unit and then returned to the gaseous environment of the incubator through the action of a low flow rate pump.
While U.S. Pat. No. 6,013,119 is one example of a VOC filter being used in conjunction with an incubator, a number of drawbacks still exist with the apparatus and method disclosed in that patent. For example, these current incubators incorporating stand-alone VOC filters use a low flow rate pump which circulates air at a rate equal to or less than about 0.3 liters per minute. The purpose of this low flow rate is to ensure that the air stream has enough residence time in the filter to maximize the filtering of contaminates. However, an increase in the time it takes a VOC filter to decontaminate one cycle of air correlates to an increased amount of time that any VOC may remain viable in the incubator prior to passing through the filter. These problems are compounded by, and some additional problems arise from, the location of the VOC filter in conjunction with currently existing incubators. As previously mentioned, these stand-alone units are segregated from the gaseous environment on the incubator chamber. Some are even located outside the incubator itself. This increases the distance the air stream must travel and thus the time necessary for filtering one cycle of air. Also, the location of the VOC filter may make it difficult to reach for repair, replacement, and/or cleaning. This results in problems of increased expense and time to perform these maintenance functions. All these problems may ultimately result in an increased degree of VOC contamination of the contents of the incubator.
In view of the above noted problems and deficiencies of incubators in general, there is a need for an incubator which provides a more accurate simulated chamber condition and which is more easily operated and maintained in the field by the end user. Further, it would be desirable to provide an incubator incorporating both a VOC and a HEPA filter which can maintain a high airflow and filtering rate and allows for easy maintenance.